Plato's Cave: The Hodgkin-Huxley Neuron
The Hodgkin-Huxley Neuron
Hodgkin & Huxley isolated a large neuron from a giant squid, and
probed it electrically to determine what its input-output function
was. They determined that the neuron consists of a cell body with a
branching network of dendrites which receive electrical input from
hundreds or thousands of neighboring neurons, and integrates this
electrical charge in the cell body. If the total charge exceeds some
threshold value, the neuron itself fires in a spasmodic series of
electrical pulses which propagate down the axon, which is the output
branch of the neuron, and that electrical signal is communicated
through a branching network to hundreds or thousands of other neurons
by way of chemical synapses.
The frequency of spiking represents the activity of the cell, which in
turn represents a sum of the signals collected from other cells,
passed through a nonlinear threshold function.
The chemical synapses can be either excitatory or inhibitory. When
they are inhibitory, then the activation of the sending neuron
suppresses activity in the receiving neuron, thus making it less
likely to exceed its own firing threshold.
This idea remains the dominant view of the computational processing
performed by the neuron, and represents the building block of which
modern theories of neural computation are constructed.
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